The Examined Japanese Utility Model Application Publication (Jikko-Hei) No. 7-2553 discloses running control for a stacker crane for an automatic warehouse in which a mark is provided at each bay of shelves so that the position of the stacker crane is corrected every time the crane passes by the bay. When the coordinates of the position of the stacker crane are called internal coordinates, The Examined Japanese Utility Model Application Publication (Jikko-Hei) No. 7-2553 corrects the internal coordinates every time the bay is passed. Consequently, accurate running control can be performed provided that running wheels do not slip or have varying diameters.
A carriage such as an overhead running vehicle starts creep running (running at very low speed) in front of a stop position so as to stop at the target stop position. For example, when a creep running speed is 0.4 cm/sec and a creep running distance is 2 cm, a running time increases by about 5 seconds.
As an example of a position sensor, the Unexamined Japanese Patent Application Publication (Tokkai-Hei) No. 2001-174206, the Unexamined Japanese Patent Application Publication (Tokkai-Hei) No. 2003-139563 and the Unexamined Japanese Patent Application Publication (Tokkai-Hei) No. 2003-156364 disclose linear sensors that use the magnetic coupling between a magnetic mark such as a magnetic substance or a nonmagnetic substance and a coil. When a plurality of detection coils are connected together in series and an alternate current is conducted through the coils, the voltage of each detection coils varies depending on the positions of the magnetic mark and the detecting coil. When the phase of the position of the detection coil with respect to the magnetic mark is defines as θ and the angular speed of the alternate current flowing through the detection coil is defined as ω, as signal proportional to sin θ, sin ωt, or cos θ, cos ωt is obtained.